Systems and methods for changing a speed of a compressor boost stage in a gas turbine

ABSTRACT

Systems and methods for changing a speed ratio between a compressor boost stage ( 12 ) and at least one power turbine ( 16 ) of a gas turbine engine ( 10 ) are described. Such a system may comprise a coupling device ( 20 ) configured to selectively transmit energy from the at least one power turbine ( 16 ) to the boost stage ( 12 ) according to at least a first speed ratio and a second speed ratio. The system may also comprise an auxiliary power device ( 22, 26 ) configured to cause a rotational speed of the boost stage ( 12 ) to change from a first speed corresponding substantially to the first speed ratio to a second speed corresponding substantially to the second speed ratio when the boost stage ( 12 ) is decoupled from the at least one power turbine ( 16 ).

TECHNICAL FIELD

The disclosure relates generally to gas turbine engines, and moreparticularly to changing a speed of a compressor boost stage in a gasturbine engine.

BACKGROUND OF THE ART

Compressor boost stages are commonly utilized to increase an overallpressure ratio in gas turbine engines. A compressor boost stagepressurizes the air upstream of a core section of an engine and istypically part of a low pressure spool of the engine driven by at leastone low pressure turbine. The coupling between the boost stage and thelow pressure spool is typically at a fixed speed ratio such that therotational speed of the boost stage may only be varied by varying therotational speed of the low pressure spool. Hence, the fixed speed ratiobetween the boost stage and the low pressure spool limits the ability tovary the overall pressure ratio during operation of the engine.

Improvement in driving of compressor boost stages in gas turbine enginesis therefore desirable.

SUMMARY

In various aspects, for example, the disclosure describes systems,devices and methods for changing a speed of a compressor boost stage ina gas turbine engine.

Thus, in one aspect, the disclosure describes systems for changing aspeed ratio between a compressor boost stage and at least one powerturbine of a gas turbine engine during operation. Such systems maycomprise: a coupling device configured to: selectively transmit energyfrom the at least one power turbine to the boost stage according to atleast a first speed ratio and a second speed ratio, and to selectivelydecouple the boost stage from the at least one power turbine andre-couple the boost stage to the at least one power turbine fortransitioning between the first speed ratio and the second speed ratio;and an auxiliary power device configured to cause a rotational speed ofthe boost stage to change from a first speed corresponding substantiallyto the first speed ratio to a second speed corresponding substantiallyto the second speed ratio when the boost stage is decoupled from thepower turbine.

In another aspect, the disclosure describes gas turbine engines. Suchgas turbine engines may comprise: a compressor boost stage, a coresection and at least one power turbine in serial flow communication; acoupling device configured to: selectively couple at least one rotor ofthe boost stage to the at least one power turbine at at least a firstspeed ratio and a second speed ratio, and to selectively decouple therotor from the at least one power turbine to permit a change inrotational speed of the rotor relative to the at least one power turbineand re-couple the rotor to the power turbine; and an auxiliary powerdevice configured to cause the rotational speed of the rotor of theboost stage to change from a first speed corresponding substantially tothe first speed ratio to a second speed corresponding substantially tothe second speed ratio when the rotor of the boost stage is decoupledfrom the power turbine.

In a further aspect, the disclosure describes methods for changing arotational speed of a compressor boost stage driven by at least onepower turbine of a gas turbine engine relative to a speed of the atleast one power turbine. Such methods may comprise: driving the booststage at a first rotational speed corresponding to a first speed ratiobetween the boost stage and the at least one power turbine via couplingbetween the boost stage and the at least one power turbine; decouplingthe boost stage from the at least one power turbine; changing therotational speed of the boost stage from the first rotational speed to asecond rotational speed substantially corresponding to a second speedratio between the boost stage and the at least one power turbine;re-coupling the boost stage to the at least one power turbine at thesecond speed ratio; and driving the boost stage at the second rotationalspeed via coupling between the boost stage and the at least one powerturbine.

Further details of these and other aspects of the subject matter of thisapplication will be apparent from the detailed description and drawingsincluded below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an axial cross-section of a gasturbine engine;

FIG. 2A is a schematic illustration of an axial cross-section of a gasturbine engine showing a boost stage coupled to a low pressure spool ofthe engine at a first speed ratio;

FIG. 2B is a schematic illustration of the engine of FIG. 2A showing theboost stage being decoupled from the low pressure spool of the engine;and

FIG. 2C is a schematic illustration of the engine of FIG. 2A showing theboost stage being coupled to the low pressure spool of the engine at asecond speed ratio.

DETAILED DESCRIPTION

Aspects of various embodiments are described through reference to thedrawings.

FIG. 1 schematically illustrates a gas turbine engine 10 of a type whichmay be provided for use in subsonic flight, generally comprising, inserial flow communication, compressor boost stage(s) 12, which mayinclude one or more compressor rotors/disks for pressurizing air; coresection(s) 14; and power turbine(s) 16. Core section(s) 14 may includeone or more compression stage(s), one or more combustors in whichcompressed air is mixed with fuel and ignited for generating an annularstream of hot combustion gases, and one or more high pressure turbines.The one or more power turbine(s) 16 may be configured to extract energyfrom the combustion gases exiting the core section(s) 14. Turbine engine10 may be suitable for use in an aircraft application and may, forexample, be configured as a turboshaft, turbofan or turboprop type ofengine. Power turbine shaft(s) 18 may, for example, be used to power ahelicopter main rotor, a propeller of a fixed-wing aircraft, or a fan ofa turbofan engine. Alternatively, turbine engine 10 may be used forground-based industrial applications such as for power generation.

An engine 10 may have a dual spool configuration but one skilled in therelevant arts will appreciate that engine 10 may not be limited to suchconfiguration. For example, engine 10 may comprise a high pressure spoolcomprising core section(s) 14 and a low pressure spool comprising powerturbine(s) 16 and boost stage(s) 12. Accordingly, power turbine(s) 16may transmit energy to boost stage(s) 12 via power turbine shaft(s) 18.Core section(s) 14 may comprise its own shaft(s) disposed coaxially withpower turbine shaft(s) 18 and may not be mechanically coupled to powerturbine shaft(s) 18. For example, power turbine shaft(s) 18 may rotatein one direction (e.g. clockwise) at one rotational speed duringoperation while core section(s) 14 rotate(s) in an opposite direction(e.g. counter-clockwise) and at a different rotational speed.

Engine 10 may be configured to permit a rotational speed of booststage(s) 12 to be changed in relation to a rotational speed of powerturbine(s) 16. Accordingly, engine 10 may comprise a system for changinga speed ratio between boost stage(s) 12 and power turbine(s) 16 duringoperation of engine 10. Such system may comprise one or more couplingdevices 20 configured to transmit energy from power turbine(s) 16 toboost stage(s) 12 via power turbine shaft(s) 18 according to at least afirst speed ratio and a second speed ratio different from the firstspeed ratio. Coupling device(s) 20 may be configured to selectivelymechanically couple and decouple boost stage(s) 12 from power turbine(s)16 of engine 10. For example, decoupling of boost stage(s) 12 from powerturbine(s) 16 may be done at the beginning of a transition period duringwhich the rotational speed of boost stage(s) 12 is either increased ordecreased relative to the rotational speed of power turbine(s) 16.Coupling device(s) 20 may then re-couple boost stage(s) 12 to powerturbine(s) 16 of engine 10 at the new speed ratio.

Auxiliary power device(s) 22 may be configured to cause the rotationalspeed of boost stage(s) 112 to change relative to power turbine(s) 16while boost stage(s) 12 is decoupled from power turbine(s) 16. Auxiliarypower device(s) 22 may be used to transmit energy to boost stage(s) 12during the transition period to cause a rotational speed of booststage(s) 12 to increase. For example, auxiliary power device(s) 22 maybe configured to transmit energy from energy source(s) 24 to booststage(s) 12. Auxiliary power device(s) 22 may also be configured tocause a decrease of the rotational speed of boost stage(s) 12 during thetransition period by, for example, causing braking of boost stage(s) 12and/or otherwise withdraw energy from boost stage(s) 12.

Auxiliary power device(s) 22 may comprise one or more energytransmission devices such as, for example, one or more air turbine(s),electric motor(s)/generator(s) and/or hydraulic motor(s) adapted toprovide energy through the application of torque or other forms of forceto boost stage(s) 12 and/or components thereof, including for examplepressurized air or other fluid impact on one or more blades of booststage(s) 12. Accordingly, energy source(s) 24 may comprise, for example,one or more sources of pressurized fluid such as air or hydraulic fluidand/or one or more sources of electrical energy such as one or morebatteries and/or one or more generator(s). Such generator(s) may bedriven by engine 10, an auxiliary power unit (APU), ram air turbine orother source(s) of motive power. For an aircraft application forexample, energy source(s) 24 may be located on-board the aircraft.

FIGS. 2A-2C schematically illustrate an exemplary representation of agas turbine engine 10, wherein auxiliary power device(s) 22 may includeair turbine(s) 26 and coupling device(s) 20 may include clutch A, clutchB and gear(s) 28. Air turbine(s) 26 may each comprise variable inletnozzle(s) 27. Air turbine(s) 26 may, for example, be coupled to booststage(s) 12 via shaft(s) 29 and gear(s) 28. The coupling of airturbine(s) 26 to boost stage(s) 12 may be selectable and may be done asrequired. Air turbine(s) 26 may, for example, be of radial or axialtype, and may be driven using pressurized air. Air turbine(s) 26 may beof a same or similar type as those typically used in air-start systemsfor turbine engines.

Energy source(s) 24 (shown in FIG. 1) may include pressurized airextracted from core section(s) 14. Such pressurized air may, forexample, be extracted from a high pressure compressor section upstreamof a combustor of core section(s) 14. Engine 10 may further comprise oneor more each of pump(s) 30, accumulator(s) 32 and/or valves 34 and 36.Pump(s) 30 may be used if desired or required to further increasepressure of the air extracted from core section(s) 14 prior to beingused to drive air turbine(s) 26. Accumulator(s) 32 may be used ifdesired or required to store an amount of pressurized air prior to beingused to drive air turbine(s) 26. Valve(s) 34 may be used to control anamount of pressurized air being extracted from core section(s) 14.Valve(s) 36 may be used to control an amount of air being delivered toair turbine(s) 26 from accumulator(s) 32 when the rotational speed ofboost stage(s) 12 is increased.

Engine 10 may also comprise inlet guide vanes 38 upstream of booststage(s) 12 and bleed valve(s) 40 for extracting compressed air fromboost stage(s) 12. Inlet guide vanes 38 may be adjustable. Bleedvalve(s) 40 may be used to supply compressed air to accessoriesassociated with or powered by engine 10 or, for example, anenvironmental control system (ECS) of an aircraft to which engine 10 maybe mounted. Alternatively, bleed valve(s) 40 may be used to bleed airfrom boost stage(s) 12 into the environment under appropriateconditions.

During operation, a system according to the disclosure may be used tochange a rotational speed of compressor boost stage(s) 12 relative to arotational speed of power turbine(s) 16 during operation of engine 10.In an aircraft application, it may be desirable to operate booststage(s) 12 at different rotational speeds during different phases offlight or under different conditions. For example, a higher rotationalspeed of boost stage(s) 12 may be desired during take-off to obtain ahigher pressure ratio when a relatively large amount of thrust and/orpower is required from engine 10. Alternatively, it may be desirable andmore efficient to operate boost stage(s) 12 at a lower rotational speedduring cruise to obtain a lower pressure ratio when a lower amount ofthrust and/or power is required from engine 10. Accordingly, the systemdescribed above may be used to change a speed ratio between booststage(s) 12 and power turbine(s) 16 during operation of engine 10.

At a particular phase of operation (e.g. flight), such as during cruisefor example, boost stage(s) 12 may be driven at a first speed bymechanically transferring energy from power turbine(s) 16 to booststage(s) 12 according to a first speed ratio via power turbine shaft(s)18, clutch A and gear(s) 28 (see FIG. 2A). Gear(s) 28 may, for example,be of speed-reducing type such that a rotational speed of boost stage(s)12 may be lower that a rotational speed of power turbine shaft(s) 18.During this phase, boost stage(s) 12 may, for example, operate at arotational speed of 11,000 rpm while power turbine shaft(s) 18 mayoperate at a rotational speed of 22,000 rpm.

Conditioned upon an increase in rotational speed of boost stage(s) 12 inrelation to power turbine(s) 16 being necessary or desired, such as inresponse to a demand for increased thrust and/or power from engine 10for example, an increase in rotational speed of boost stage(s) 12relative to power turbine(s) 16 may be initiated. The speed increase ofboost stage(s) 12 may be achieved over a transition period during whichboost stage(s) 12 may be temporarily decoupled from power turbineshaft(s) 18. The decoupling of boost stage(s) 12 from power turbineshaft(s) 18 may, for example, be achieved by releasing clutch A whileclutch B may already be released (see FIG. 2B).

In order to increase the rotational speed of boost stage(s) 12,auxiliary power device(s) 22, 26 may be used to transfer energy to booststage(s) 12 to increase the rotational speed of boost stage(s) 12 from afirst speed to a second speed while boost stage(s) 12 may be temporarilydecoupled from power turbine shaft(s) 18. Energy transfer from auxiliarypower device(s) 22, 26 to boost stage(s) 12 may be done mechanically viashaft(s) 29 and gear(s) 28. Air turbine(s) 26 may transfer energy fromcore section(s) 14 to boost stage(s) 12. Accordingly, pressurized airmay be extracted from core section(s) 14 and used to drive airturbine(s) 26. The amount of pressurized air extracted from coresection(s) 14 may be controlled via valve(s) 34. Pump(s) 30 may be usedif necessary or desired to further pressurize the air prior to drivingair turbine(s) 26. Accumulator(s) 32 may also be used to store somepressurized air prior to driving air turbine(s) 26.

Once boost stage(s) 12 has reached the second (i.e. increased) speed,which may substantially correspond to a second speed ratio available viaclutch B, boost stage(s) 12 may be re-coupled to power turbine shaft(s)18 via clutch B and the driving of boost stage(s) 12 via powerturbine(s) 16 may be resumed (see FIG. 2C). Clutch B may be configuredto mechanically couple boost stage(s) 12 directly to power turbineshaft(s) 18 at a one to one speed ratio. For example, when clutch B isengaged, clutch A may be disengaged and both boost stage(s) 12 and powerturbine(s) 16 may be operating at a rotational speed of 22,000 rpm.

The system described above may also be used to decrease the rotationalspeed of boost stage(s) 12 relative to power turbine(s) 16. For example,while boost stage(s) 12 may be driven via clutch B (see FIG. 2C) at arelatively high rotational speed under appropriate conditions andconditioned upon a decrease in rotational speed of boost stage(s) 12relative to power turbine(s) 16 being necessary or desired, a decreasein rotational speed of boost stage(s) 12 may be initiated. Similarly tothe procedure described above, the speed decrease of boost stage(s) 12relative to power turbine(s) 16 may be achieved over a transition periodduring which boost stage(s) 12 may be temporarily decoupled from powerturbine shaft(s) 18. The decoupling of boost stage(s) 12 from powerturbine shaft(s) 18 may be achieved, for example, by releasing clutch Bwhile clutch A may already be released (see FIG. 2B).

In order to decrease the rotational speed of boost stage(s) 12,auxiliary power device(s) 22, 26 may be used to cause braking of booststage(s) 12 or otherwise withdraw energy from boost stage(s) 12 todecrease the rotational speed of boost stage(s) 12 from a first speed toa second speed while boost stage(s) 12 may be temporarily decoupled frompower turbine shaft(s) 18. Braking may be achieved by using booststage(s) 12 to drive air turbine(s) 26 via shaft(s) 29 while the inletflow and pressure to air turbine(s) 26 is controlled by adjustingvariable inlet nozzle(s) 27 and consequently adjusting a resistanceapplied to boost stage(s) 12 by air turbine(s) 26. Auxiliary powerdevice(s) 22 may include other braking means suitable for decreasing therotational speed of boost stage(s) 12.

Once boost stage(s) 12 has reached the second (i.e. reduced) speed,which may substantially correspond to a second speed ratio available viaclutch A, boost stage(s) 12 may be re-coupled to power turbine shaft(s)18 via clutch A and gear(s) 28 and the driving of boost stage(s) 12 viapower turbine(s) 16 may be resumed (see FIG. 2A). As explained above,clutch A may be configured to mechanically couple boost stage(s) 12 topower turbine(s) 16 via gear(s) 28 and thereby allow boost stage(s) torotate at a lower speed in comparison with mechanical coupling viaclutch B.

During the speed transition of boost stage(s) 12 between the first speedand the second speed (whether increased or reduced), inlet guide vanes38 and/or bleed valve(s) 40 may be adjusted to control (i.e. increase ordecrease) a resistance on boost stage(s) 12 and thereby facilitate thespeed transition. For example, during a speed increase boost stage(s)12, inlet guide vanes 38 and bleed valve(s) 40 may be adjusted todecrease the resistance on boost stage(s) 12 and thereby assist inincreasing the rotational speed of boost stage(s) 12. Conversely, duringa speed decrease of boost stage(s) 12, inlet guide vanes 38 and bleedvalves(s) 40 may be adjusted to increase the resistance on booststage(s) 12 and thereby assist in braking boost stage(s) 12. In someaircraft applications, it may be desirable that the transition ofrotational speed of boost stage(s) 12 between the first speed and thesecond speed be performed during a relatively short period of time (e.g.around 2 seconds).

The methods described above may be executed and controlled by a controlsystem of engine 10 and may be initiated in response to an action (e.g.request or command) by an operator of engine 10 such as a pilot of anaircraft for example. The control system of engine 10 may include orform part of a Full Authority Digital Engine Control (FADEC) which may,for example, comprise one or more digital computer(s) or other dataprocessors, sometimes referred to as electronic engine controller(s)(EEC) and related accessories that control at least some aspects ofperformance of engine 10. The control system may include one or moremicrocontrollers or other suitably programmed or programmable logiccircuits.

The above description is meant to be exemplary only, and one skilled inthe relevant arts will recognize that changes may be made to theembodiments described without departing from the scope of the inventiondisclosed. For example, coupling device(s) 20 may be configureddifferently than the exemplary configuration of FIGS. 2A-2C. Forexample, both energy transfer paths via clutch A and clutch B may eachcomprise gear(s) 28 that provide a different speed ratio (e.g. reducingor augmenting) between boost stage(s) 12 and power turbine shaft(s) 18so as to achieve the desired speed ratios via clutch A and clutch B.Alternatively, in various embodiments, coupling device(s) 20 may onlyinclude a single clutch, such as clutch A for example, while gear(s) 28may be configured to provide two or more energy transfer paths atdifferent speed ratios.

Still other modifications which fall within the scope of the presentinvention will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

1. A system for changing a speed ratio between a compressor boost stageand at least one power turbine of a gas turbine engine during operation,the system comprising: a coupling device configured to: selectivelytransmit energy from the at least one power turbine to the boost stageaccording to at least a first speed ratio and a second speed ratio, andto selectively decouple the boost stage from the at least one powerturbine and re-couple the boost stage to the at least one power turbinefor transitioning between the first speed ratio and the second speedratio; and an auxiliary power device configured to cause a rotationalspeed of the boost stage to change from a first speed correspondingsubstantially to the first speed ratio to a second speed correspondingsubstantially to the second speed ratio when the boost stage isdecoupled from the power turbine.
 2. The system as defined in claim 1,wherein the auxiliary power device is configured to transmit energy tothe boost stage to cause an increase in the rotational speed of theboost stage.
 3. The system as defined in claim 1, wherein the auxiliarypower device is configured to cause braking of the boost stage to causea decrease in the rotational speed of the boost stage.
 4. The system asdefined in claim 1, wherein the auxiliary power device comprises an airturbine.
 5. The system as defined in claim 4, wherein the air turbine isoperably coupled to receive pressurized air from a core section of theengine.
 6. The system as defined in claim 5, comprising a pump topressurize the air from the core section of the engine prior to use bythe air turbine.
 7. The system as defined in claim 4, comprising anaccumulator to store the pressurized air for use by the air turbine. 8.The system as defined in claim 1, wherein the coupling device comprisesa first clutch to engage the boost stage to the at least one powerturbine at the first speed ratio and a second clutch to engage the booststage to the at least one power turbine at the second speed ratio.
 9. Agas turbine engine comprising: a compressor boost stage, a core sectionand at least one power turbine in serial flow communication; a couplingdevice configured to: selectively couple at least one rotor of the booststage to the at least one power turbine at at least a first speed ratioand a second speed ratio, and to selectively decouple the rotor from theat least one power turbine to permit a change in rotational speed of therotor relative to the at least one power turbine and re-couple the rotorto the power turbine; and an auxiliary power device configured to causethe rotational speed of the rotor of the boost stage to change from afirst speed corresponding substantially to the first speed ratio to asecond speed corresponding substantially to the second speed ratio whenthe rotor of the boost stage is decoupled from the power turbine. 10.The gas turbine engine as defined in claim 9, wherein the couplingdevice comprises a first clutch to engage the rotor of the boost stageto the at least one power turbine at the first speed ratio and a secondclutch to engage the rotor of the boost stage to the at least one powerturbine at the second speed ratio.
 11. The gas turbine engine as definedin claim 9, wherein the auxiliary power device is configured to transmitenergy from the core section of the engine to the rotor of the booststage to cause an increase in rotational speed of the rotor.
 12. The gasturbine engine as defined in claim 9, wherein the auxiliary power devicecomprises an air turbine.
 13. The gas turbine engine as defined in claim12, wherein the air turbine is operably coupled to receive pressurizedair from the core section of the engine.
 14. The gas turbine engine asdefined in claim 13, comprising an accumulator for storing pressurisedair for use by the air turbine.
 15. A method for changing a rotationalspeed of a compressor boost stage driven by at least one power turbineof a gas turbine engine relative to a speed of the at least one powerturbine, the method comprising: driving the boost stage at a firstrotational speed corresponding to a first speed ratio between the booststage and the at least one power turbine via coupling between the booststage and the at least one power turbine; decoupling the boost stagefrom the at least one power turbine; changing the rotational speed ofthe boost stage from the first rotational speed to a second rotationalspeed substantially corresponding to a second speed ratio between theboost stage and the at least one power turbine; re-coupling the booststage to the at least one power turbine at the second speed ratio; anddriving the boost stage at the second rotational speed via couplingbetween the boost stage and the at least one power turbine.
 16. Themethod as defined in claim 15, comprising transferring energy to theboost stage to cause the rotational speed of the boost stage to increasein relation to the at least one power turbine while the boost stage isdecoupled from the at least one power turbine.
 17. The method as definedin claim 15, comprising adjusting at least one of inlet guide vanes anda bleed valve to adjust a resistance on the boost stage.
 18. The methodas defined in claim 16, comprising extracting pressurized air from acore section of the turbine engine and using the pressurized air todrive an air turbine coupled to the boost stage to cause the rotationalspeed of the boost stage to increase in relation to the at least onepower turbine.
 19. The method as defined in claim 18, comprisingpressurizing the air extracted from the core section prior to drivingthe air turbine.
 20. The method as defined in claim 15, comprisingbraking the boost stage to cause the rotational speed of the boost stageto decrease in relation to the at least one power turbine while theboost stage is decoupled from the at least one power turbine.